A developing device is provided in an image forming apparatus, such as a laser printer or the like. The developing device supplies toner accommodated in a toner accommodating chamber to a developing roller through a supply roller to be attached on an electrostatic latent image on the surface of a photosensitive drum, thereby forming a toner image. This toner image formed on the photosensitive drum is transferred to a sheet transported and is then fixed to the sheet by a fixing device provided in the image forming apparatus main body. Accordingly, an image forming operation is completed.
However, in the image forming apparatus, toner which is accommodated in the developing device is deteriorated with the operation time of the developing device, so that an image quality is deteriorated.